Technical Field
The present disclosure relates to a power supply apparatus. More particularly, the present disclosure relates to a frequency uttering control mechanism in a power supply apparatus.
Description of Related Art
In a typical power supply apparatus, a main switch controlled by a control chip is conventionally operated with a constant frequency, or operated in a threshold mode that frequency varies along with input characteristics and/or output characteristics.
However, since electro-magnetic interference (EMI) generated by the power supply apparatus operated with the constant frequency is conventionally gathered where an integer multiple of a switch frequency is applied, EMI characteristics of the power supply apparatus may be difficult to satisfy a required standard. This also results in that the power supply apparatus usually requires a EMI filtering device with larger size, thus increasing high manufacturing cost.
On the other hand, for the power supply apparatus operated in the threshold mode, with variable-frequency control or pulse frequency modulation (PFM), the power supply apparatus can be operated in various variable-frequency modes, but the frequency changes in these modes will depend on the restriction conditions such as input voltage, output voltage and so on. When an input voltage thereof is constant and an output voltage thereof is provided for a constant load, switching frequency in the aforementioned variable-frequency modes keeps constant, and this results in that EMI generated by a switch device is still gathered where an integer multiple of the switching frequency is applied.
Based on the aforementioned situation, the EMI characteristics of the power supply apparatus cannot be improved effectively in the conventional art, and moreover, adjustment cannot be made according to the real input/output of the power supply apparatus in order to effectively improve the EMI characteristics.